This invention relates to modified organopolysiloxanes and a method of increasing the flex life of organopolysiloxanes, and more particularly, to improved silicone elastomers having olefinic unsaturation and a method of improving the flex life of silicone elastomers having olefinic unsaturation.
Modified organopolysiloxanes have been prepared in the prior art by polymerizing monomers containing aliphatic unsaturation in the presence of organopolysiloxanes containing terminal hydroxyl or hydrolyzable groups and free radical initiators. Other modified organopolysiloxanes have been made by gradually adding a mixture of monomers and free radical initiators to the preheated organopolysiloxanes, and in other cases, free radical initiators have been gradually added to a preheated mixture containing an organic polysiloxane and an organic monomer having aliphatic unsaturation. Various of these modified organopolysiloxanes have a tendency to shrink during curing, and accordingly, they are undesirable when the composition is used as a molding or potting composition. In other instances the agent used to modify the organopolysiloxane may have an adverse effect on such properties as hardness, tensile strength, elongation, elasticity, tear, flex and the like.
Other materials have also been used to modify various organopolysiloxanes. In U.S. Pat. No. 4,014,851 vinylorganopolysiloxane compositions have been modified by filling them with polyolefin wherein monomers having aliphatic unsaturation are polymerized in the presence of vinylorganopolysiloxanes and free radical initiators to improve the properties of the vinyl organopolysiloxanes. In certain other cases, improvements in properties have been attempted by grafting organopolysiloxanes, that is, providing organopolysiloxanes which are chemically grafted with polymeric side chains. However, while graft modified organopolysiloxanes have some desirable properties, they are inadequate in others, such as, poor solvent resistance and the like, and accordingly, they have not met with complete satisfaction. In U.S. Pat. No. 4,014,851, the finely-divided solid particles of homopolymer or copolymer which are formed in-situ, appear to act as reinforcing or semi-reinforcing fillers or in some cases extending fillers, for the vinyl organopolysiloxane matrix material resulting in an improved stronger silicone elastomer product. Although the compositions formed in U.S. Pat. No. 4,014,851 have improved properties and appear to have overcome the prior art deficiencies, it is still advantageous to improve various properties of the organopolysiloxanes.